1. Field of the Invention
The present invention relates to a control system wherein closed-loop control and duty cycle control are combined.
2. Description of the Prior Art
In the temperature control of a refrigerator system or the like, a closed-loop system employing a thermostat is of frequent use. That system provides ON/OFF control of the operation of a refrigerator system by means of a thermostat provided therein to control the temperature of the refrigerator system at a desired temperature. If the thermostat therein is provided with a larger value of differential, or a hysteresis lag in the ON/OFF operation, either the duration of the controlled temperature values, or the deviation of the temperature from a desired temperature, will become the larger. If, on the other hand, the differential is set at a smaller value to make the duration smaller, the ON/OFF operation will alternate so frequently that the refrigerator system is put under a severe operating condition. Thus, the setting of the differential is quite delicate and troublesome. Additionally, the ON/OFF control is executed regardless of the ambient temperature is spite of the fact that an ambient temperature change due to change of season or the like has an effect on the object of the control. Such being the case, that type of control has not been wholly satisfactory.